Question: Which of these numbers is composite? ${2,\ 31,\ 71,\ 77,\ 89}$
Answer: A composite number is a number that has more than two factors (including 1 and itself). 2, 31, 71, and 89 each have only two factors. The factors of 77 are 1, 7, 11, and 77. Thus, 77 is the composite number.